The present invention relates to an apparatus for reproducing video information recorded on a recording medium such as a recording disk.
FIG. 5 shows a conventional information reproducer in which an RF (high frequency) signal including video information read from a recording disk 2 through a pickup 1 is supplied to a demodulation circuit 3 made of an FM demodulator and so forth. A video signal is demodulated by the demodulation circuit 3 and then supplied to an A/D converter 4 and a synchronizing signal separation circuit 5 which separates horizontal and vertical synchronizing signals from the video signal. The horizontal synchronizing signal sent out from the synchronizing signal separation circuit 5 is supplied to a phase comparison circuit 6 and a writing clock signal generation circuit 9. In the phase comparison circuit 6, the phase of the horizontal synchronizing signal and that of a reference signal r sent out from a quartz oscillator or the like (not shown in the drawing) and having a prescribed frequency are compared with each other so that a phase difference detection signal corresponding to the difference between the phases of the compared signals is generated. The phase difference detection signal is supplied as a spindle error signal to a servo-amplifier 7. A spindle motor 8 for rotating the recording disk 2 is supplied with the output from the servo-amplifier 7 so that the rotary speed of the recording disk is controlled. The writing clock signal generation circuit 9 generates clock pulses synchronized with the horizontal synchronizing signal. The clock pulse sent out from the writing clock signal generation circuit 9 is supplied as a sampling pulse to the A/D converter 4 and as a writing command signal to a variable delay circuit 10. In the A/D converter 4, the video signal is sampled through the use of the clock pulse so that a digital signal corresponding to a value obtained by the sampling is generated. The digital signal is supplied from the A/D converter 4 to the variable delay circuit 10 to which reading clock pulses sent out from a reading clock signal generation circuit 11 and having a prescribed frequency are supplied as a reading command signal. For example, the variable delay circuit 10 is made of a first-in first-out memory so that input data are sequentially written into the memory in accordance with the writing command signal and the written data are sequentially read from the memory in the order of writing, in accordance with the reading command signal. In the variable delay circuit 10, the signal delay time for the input data is changed depending on the time-axis error, to correct the error. The output data from the variable delay circuit 10 are supplied to a memory 12 to which address data and a mode control signal are supplied from a memory controller 13. The reading clock pulses and a still picture reproduction command signal a sent out from a control unit (not shown in the drawing) are supplied to the memory controller 13. The memory controller 13 sends out the mode control signal and the address data so that data are sequentially written into the memory 12 and the written data are sequentially read therefrom in the order of writing, in accordance with the reading clock pulses, when the still picture reproduction command signal a is not present; and such that the data written in the memory 12 are sequentially read therefrom in accordance with the reading clock pulses when the still picture reproduction command signal a is present. The data read from the memory 12 are supplied to a D/A converter 14 in which the data are sequentially converted into analog signals through the use of the reading clock pulses. The analog signals are sent out as reproduced video signals from the D/A converter 14.
When the still picture reproduction command signal is not sent out from the control unit, namely, when the signal is not present, the video signals sent out from the demodulation circuit 3 are written into the memory 12 through the A/D converter 4 and the variable delay circuit 10 and thereafter sequentially read from the memory in the order of writing so that the information recorded on the recording disk 2 is sequentially reproduced in the order of the reading of the information from the disk.
When the still picture reproduction command signal is sent out from the control panel, namely, when the signal is present, the data written in the memory 12 are repeatedly read therefrom as the contents of the memory are not rewritten, so that a still picture is reproduced.
If the memory 12 has the capacity to store data corresponding to one frame of video signals, the cost of the memory is high and the still picture reproduced by repeatedly reading the data (one frame of video signals) is distorted. For this reason, the memory 12 actually has the capacity to store an amount of data corresponding to one field of video signals. As a result, the mutually corresponding portions of the regions made by the scanning lines of the first and the second fields which form the still picture in the conventional information reproducer are the same as each other in the luminance and so forth. Therefore, the portions .alpha. which belong to the region made by the plural scanning lines of the first field and which intersect a prescribed vertical line, and portions .beta. which belong to the region made by the plural scanning lines of the second field and which intersect the vertical line, have luminances as shown in FIG. 6, and the center c of the picture formed by the first field and that d of the picture made by the second field do not coincide with each other. For this reason, the conventional information reproducer has a drawback in that half-line-interval vertical jitter is caused.
When an oblique line should be reproduced as shown in FIG. 7(A), a still picture reproduced from video signals read from the recording disk 2 and thereafter sent out from the D/A converter 14 becomes conspicuously zigzagged as shown in FIG. 7(B), where the .gamma.'s are portions of a region made by the scanning lines of a first field (shown by solid lines) and the .delta.'s are portions of a region made by the scanning lines of a second field (shown by dashed lines). This is another drawback of the conventional information reproducer.
In order to eliminate the above-mentioned drawbacks, it has been considered to provide a 1-H delay line which functions to delay data read from the memory 12 by one horizontal scanning period in the conventional information reproducer. Data obtained by calculating the average of the instantaneous value of the input to the 1-H delay line and the output therefrom would be supplied to the D/A converter 14 instead of the data read from the memory 12, in every other field. However, since the 1-H delay line is expensive, there is still a drawback in that the cost of production of the conventional information reproducer increases.